Method, apparatus and circuitry for droplet ejection

ABSTRACT

A droplet ejection apparatus including a droplet deposition head, actuating circuitry and head controller circuitry. The droplet deposition head having an array of actuating elements and a corresponding array of nozzles. The actuating circuitry applies drive waveforms to the actuating elements causing the ejection of fluid in the form of droplets through the array of nozzles and onto deposition media, which are moved relative to the droplet deposition head. The head controller circuitry is configured to receive an input set of ejection data, generate a series of sub-sets of ejection data based on the input set, and send the series of sub-sets of ejection data to the actuating circuitry. The actuating circuitry is further configured so as to, for each sub-set of ejection data, apply drive waveforms to the actuating elements such that they repeatedly eject droplets from one or more nozzles, thus depositing successive rows of droplets. The one or more nozzles and the sizes of the droplets ejected therefrom are determined by the current sub-set of ejection data. Each of the one or more nozzles ejecting droplets with a substantially constant frequency of 1/T. The apparatus is further configured to receive deposition media speed data, which indicates the current speed of relative movement of the head with respect to the deposition media. The apparatus is further configured such that the head switches from ejecting droplets in accordance with a current sub-set of ejection data to ejecting droplets in accordance with a consecutive sub-set of ejection data in the series at a time determined in accordance with the media speed data, with the time interval between starting ejecting droplets in accordance with successive sub-sets of ejection data varying inversely with the current speed of relative movement of the droplet deposition head.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is continuation of U.S. patent application Ser. No.16/650,235, filed Mar. 24, 2020, which is a 371 of internationalapplication no. PCT/GB2018/052722, filed Sep. 25, 2018, which is basedon and claims the benefit of foreign priority under 35 U.S.C. § 119 toGB Application No. 1715513.6, filed Sep. 25, 2017. This entire contentsof the above-referenced applications are expressly incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for dropletejection, as well as to circuitry therefor. It may find particularlybeneficial application in a printer including a printhead, such as aninkjet printhead, and circuitry therefor.

BACKGROUND TO THE INVENTION

Droplet deposition heads are now in widespread usage, whether in moretraditional applications, such as inkjet printing, or in 3D printing, orother materials deposition or rapid prototyping techniques. Accordingly,the fluids may have novel chemical properties to adhere to newsubstrates and increase the functionality of the deposited material.

Recently, inkjet printheads have been developed that are capable ofdepositing ink directly onto ceramic tiles, with high reliability andthroughput. This allows the patterns on the tiles to be customized to acustomer's exact specifications, as well as reducing the need for a fullrange of tiles to be kept in stock.

In other applications, inkjet printheads have been developed that arecapable of depositing ink directly on to textiles. As with ceramicsapplications, this may allow the patterns on the textiles to becustomized to a customer's exact specifications, as well as reducing theneed for a full range of printed textiles to be kept in stock.

In still other applications, droplet deposition heads may be used toform elements such as colour filters in LCD or OLED elements displaysused in flat-screen television manufacturing.

So as to be suitable for new and/or increasingly challenging depositionapplications, droplet deposition heads continue to evolve andspecialise. However, while a great many developments have been made,there remains room for improvements in the field of droplet depositionheads.

SUMMARY

Aspects of the invention are set out in the appended claims.

The following disclosure describes a droplet ejection apparatuscomprising: a droplet deposition head comprising an array of actuatingelements and a corresponding array of nozzles; actuating circuitry,configured to apply drive waveforms to said actuating elements, therebycausing the ejection of fluid in the form of droplets through said arrayof nozzles onto deposition media, which are moved relative to the head;and head controller circuitry, configured to: receive an input set ofejection data; generate a series of sub-sets of ejection data based onthe input set; and send said series of sub-sets of ejection data to saidactuating circuitry.

The actuating circuitry is further configured so as to, for each sub-setof ejection data, apply drive waveforms to said actuating elements suchthat they repeatedly eject droplets from one or more nozzles, thusdepositing successive rows of droplets, the one or more nozzles and thesizes of the droplets ejected therefrom being determined by the currentsub-set of ejection data, each of the one or more nozzles ejectingdroplets with a substantially constant frequency of 1/T. The apparatusis configured to receive deposition media speed data, which indicatesthe current speed of relative movement of the head with respect to thedeposition media. The apparatus is further configured such that the headswitches from ejecting droplets in accordance with a current sub-set ofejection data to ejecting droplets in accordance with a consecutivesub-set of ejection data in the series at a time determined inaccordance with said media speed data, with the time interval betweenstarting ejecting droplets in accordance with successive sub-sets ofejection data varying inversely with the current speed of relativemovement of the head.

The following disclosure also describes controller circuitry for adroplet deposition head that comprises an array of actuating elementsand a corresponding array of nozzles, the controller circuitryconfigured to: receive an input set of ejection data; generate a seriesof sub-sets of ejection data based on the input set; receive depositionmedia speed data, which indicates the current speed of relative movementof the head with respect to the deposition media; and send said seriesof sub-sets of ejection data and respective ejection commands toactuating circuitry for the droplet deposition head, the ejectioncommands being sent at a time determined in accordance with the currentspeed of relative movement of the head with respect to the depositionmedia as indicated in said deposition media speed data, the timeinterval between sending successive sub-sets of ejection data varyinggenerally inversely with the current speed of relative movement of thehead.

The following disclosure further describes actuation control circuitryfor a droplet deposition head that comprises an array of actuatingelements and a corresponding array of nozzles, the actuation controlcircuitry being configured to: receive a series of sub-sets of ejectiondata, each of which is based on an input set of ejection data; receivetrigger signals; for each of said sub-sets of ejection data, repeatedlysending a corresponding set of actuation commands to waveform generatingcircuitry for the droplet deposition head, each set of actuationcommands causing the waveform generating circuitry to apply drivewaveforms to said actuating elements such that they eject droplets fromone or more nozzles, the one or more nozzles and the sizes of thedroplets ejected therefrom being determined by the corresponding sub-setof ejection data, the repeated sending of the set of actuation commandscausing each of the one or more nozzles to repeatedly eject dropletswith a substantially constant frequency of 1/T, thus depositingsuccessive rows of droplets; switch from sending actuation commands inaccordance with a current sub-set of ejection data to sending actuationcommands in accordance with a consecutive sub-set of ejection data inthe series at a time determined in accordance with said trigger signals.

Still further, the following disclosure describes actuating circuitryfor a droplet deposition head that comprises an array of actuatingelements and a corresponding array of nozzles, the actuating circuitrybeing configured to: receive a series of sub-sets of ejection data, eachof which is based on an input set of ejection data; receive triggersignals; generate drive waveforms for said actuating elements so as tocause the repeated ejection of droplets from one or more nozzles, thusdepositing successive rows of droplets, the one or more nozzles and thesizes of the droplets ejected therefrom being determined by the currentsub-set of ejection data, each of the one or more nozzles ejectingdroplets with a substantially constant frequency of 1/T; switch fromgenerating drive waveforms in accordance with a current sub-set ofejection data to generating drive waveforms in accordance with aconsecutive sub-set of ejection data in the series at a time determinedin accordance with said trigger signals.

Furthermore, the following disclosure describes a method for depositingdroplets using a droplet deposition head comprising an array ofactuating elements and a corresponding array of nozzles, the methodcomprising: receiving an input set of ejection data; generating a seriesof sub-sets of ejection data based on the input set; receivingdeposition media speed data, which indicates the current speed ofrelative movement of the head with respect to deposition media; andoperating the head according to each sub-set of ejection data in turn,while moving the head relative to the deposition media, such operatingcomprising: for each sub-set of ejection data, repeatedly ejectingdroplets from one or more nozzles within said array so as to depositsuccessive rows of droplets, the one or more nozzles and the sizes ofthe droplets ejected therefrom being determined by the current sub-setof ejection data, each of the one or more nozzles ejecting droplets witha substantially constant frequency of 1/T; and switching from ejectingdroplets in accordance with one sub-set of ejection data to ejectingdroplets in accordance with the consecutive sub-set of ejection data ata time determined in accordance with the current speed of relativemovement of the head with respect to the deposition media as indicatedby said media speed data, the time interval between starting ejectingdroplets in accordance with successive sub-sets of ejection data varyinginversely with the current speed of relative movement of the head.

To meet the material needs of diverse applications, a wide variety ofalternative fluids may be deposited by droplet deposition heads asdescribed herein. For instance, a droplet deposition head may ejectdroplets of ink that may travel to a sheet of paper or card, or to otherreceiving media, such as textile or foil or shaped articles (e.g. cans,bottles etc.), to form an image, as is the case in inkjet printingapplications, where the droplet deposition head may be an inkjetprinthead or, more particularly, a drop-on-demand inkjet printhead.

Alternatively, droplets of fluid may be used to build structures, forexample electrically active fluids may be deposited onto receiving mediasuch as a circuit board so as to enable prototyping of electricaldevices.

In another example, polymer containing fluids or molten polymer may bedeposited in successive layers so as to produce a prototype model of anobject (as in 3D printing).

In still other applications, droplet deposition heads might be adaptedto deposit droplets of solution containing biological or chemicalmaterial onto a receiving medium such as a microarray.

Droplet deposition heads suitable for such alternative fluids may begenerally similar in construction to printheads, with some adaptationsmade to handle the specific fluid in question.

Droplet deposition heads as described in the following disclosure may bedrop-on-demand droplet deposition heads. In such heads, the pattern ofdroplets ejected varies in dependence upon the input data provided tothe head.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now directed to the drawings, in which:

FIG. 1 is a block diagram that illustrates schematically a dropletdeposition apparatus according to a first example embodiment;

FIG. 2A is a diagram illustrating the points in time at which dropletsare ejected by the droplet deposition apparatus of FIG. 1 in accordancewith a particular series of sub-sets of ejection data;

FIG. 2B is a diagram illustrating the locations on the substrate wherethe droplets whose ejection is illustrated in FIG. 2A are deposited;

FIG. 3A is a diagram illustrating the points in time at which dropletsare ejected by the droplet deposition apparatus of FIG. 1 in accordancewith the same series of sub-sets of ejection data as in FIGS. 3A and 3B,but in a situation where the speed of relative movement of the head withrespect to the deposition media varies in a different way with respectto time;

FIG. 3B is a diagram illustrating the locations on the substrate wherethe droplets whose ejection is illustrated in FIG. 3A are deposited;

FIG. 4 is a block diagram that illustrates a further example embodimentof a droplet deposition apparatus, which includes a media transportsystem and a server;

FIG. 5 is a block diagram that illustrates a further example embodimentof a droplet deposition apparatus, where the actuating circuitry isprovided by two separate components; and

FIG. 6 is a block diagram that illustrates a still further exampleembodiment of a droplet deposition apparatus, where the actuatingcircuitry is provided by two separate components, but in a differentarrangement to that shown in FIG. 5.

DETAILED DESCRIPTION OF THE DRAWINGS

Attention is firstly directed to FIG. 1, which is a block diagram thatillustrates schematically a droplet ejection apparatus according to anexample embodiment.

As may be seen from FIG. 1, the droplet deposition apparatus includes adroplet deposition head 10, as well as associated actuating circuitry100 and head controller circuitry 200. In the particular exampleembodiment shown in FIG. 1, the actuating circuitry 100 forms part ofthe head 10; however, this is not essential and in other embodimentsactuating circuitry 100 may be provided separately from (off-board) thehead 10.

As may also be seen from FIG. 1, the head 10 includes an array ofactuating elements 22(1)-22(N) and a corresponding array of nozzles18(1)-18(N). While in the particular example embodiment shown in FIG. 1a respective nozzle 18 is provided for each actuating element 22, thisis by no means essential; for instance, each actuating element 22 couldinstead be provided with two (or more) nozzles, or, conversely, two (orperhaps more) actuating elements 22 could be provided for each nozzle 18to cause droplet ejection therefrom.

The actuating elements 22 may be of any suitable type, such as, forexample, a piezoelectric actuating element. Nonetheless, other types ofelectromechanical actuating elements, such as electrostatic actuatingelements, could be utilised. Indeed, the actuating elements need not beelectromechanical: they might, for example, be thermal actuatingelements, such as resistive elements.

Though not illustrated in FIG. 1, the head may include a respectivefluid chamber for each actuating element 22, thus providing an array offluid chambers, with each actuating element 22 causing the ejection offluid from the corresponding fluid chamber. Where an electromechanicalactuating element 22 is employed, this may function by deforming a wallbounding the corresponding one of the chambers. Such deformation may inturn increase the pressure of the fluid within the chamber and therebycause the ejection of droplets of fluid from the nozzle. Each suchdeformable wall might, for example, be provided by a deformablemembrane, or it might separate neighbouring chambers within the arrayand include one of the electromechanical actuating elements 22.

Nonetheless, it is by no means essential that the head includes arespective fluid chamber for each actuating element 22, and in otherembodiments a common fluid chamber might be shared by multiple actuatingelements 22 and multiple nozzles 18.

In terms of its functionality, the actuating circuitry 100 is configuredto apply drive waveforms to the actuating elements 22(1)-22(N) of thehead 10, thereby causing the ejection of fluid in the form of dropletsthrough the array of nozzles 18(1)-18(N). This is apparent in FIG. 1from the droplets illustrated adjacent nozzles 18(2), 18(3), 18(N−1) and18(N). While droplets are ejected, the head 10 will move relative todeposition media (for example, paper, labels, ceramic tiles, bottlesetc.) so as to form a pattern of deposited droplets thereon.

Considering now the functionality of the head controller circuitry 200,as is apparent from FIG. 1 this circuitry 200 is configured to receivean input set of ejection data 610. The head controller circuitry 200uses this input set 610 to generate sub-sets of ejection data210(1)-210(3). More particularly, it generates a series of sub-sets ofejection data 210(1)-210(3) based on the input set 610. The headcontroller circuitry 200 then sends this series of sub-sets of ejectiondata to the actuating circuitry 100, with the actuating circuitrycausing the deposition of droplets based on each of the sub-sets ofejection data 210(1)-210(3) in the series, in turn. Such deposition ofdroplets will now be described in more detail with reference to FIGS.2A-2B and 3A-3B.

Attention is directed firstly to FIG. 2A, which is a diagram showing, onthe vertical axis, nozzles 18(1)-18(7) within the nozzle array of thehead 10, and, on the horizontal axis, time. The point in time at which adroplet is ejected from a nozzle is indicated by a black circle in thedrawing. In addition, at the top of the diagram a number of arrowsindicate the respective moments at which each sub-set of ejection data210(1)-210(5) is received by the actuating circuitry 100.

FIG. 2B is a similar diagram to FIG. 2A, except in that, whereas theblack circles in FIG. 2A indicated the point in time at which ejectionoccurs from a nozzle 18(1)-18(7), the black circles in FIG. 2B indicatethe point in space at which a droplet from a particular nozzle18(1)-18(7) is deposited. Accordingly, the horizontal axis in FIG. 2Bcorresponds to distance in the direction of relative movement of thehead 10 with respect to the deposition media.

It should be appreciated that droplet deposition apparatus as describedherein are susceptible of use with a wide range of deposition media,such as: paper; labels; ceramic tiles; cans, bottles and other shapedarticles; and printed circuit boards.

As is apparent from FIG. 2A, for each sub-set of ejection data210(1)-210(5), the actuating circuitry 100 causes the repeated ejectionof droplets from one or more nozzles 18(1)-18(7). The particular nozzlesthat eject droplets are determined by the respective one of the sub-setsof ejection data 210(1)-210(5), as are the sizes of the droplets ejectedtherefrom. For instance, in response to sub-set 210(1) of ejection data,the actuating circuitry 100 causes nozzles 18(1), 18(2), 18(6) and 18(7)to eject droplets.

As is also apparent from FIG. 2A, each nozzle that ejects droplets doesso every T seconds, i.e. with a substantially constant frequency of 1/T.As may be appreciated from FIG. 2B, such repeated ejection of dropletsleads to successive rows of droplets being deposited on the print media.

Moreover, in the particular examples shown in FIGS. 2A-2B and 3A-3B,this ejection frequency is maintained for nozzles that eject droplets inaccordance with successive sub-sets of ejection data (e.g. nozzle 18(3),which ejects droplets in accordance with sub-sets 210(3) and 210(4)).Thus, the time interval between the final droplet resulting from theearlier set and the first droplet resulting from the later set is equalto T.

Returning briefly to FIG. 1, as is shown, the droplet depositionapparatus is configured to receive deposition media speed data 310,which indicates the current speed of relative movement of the head 10with respect to the deposition media. Reference is made here to thespeed of relative movement of the head 10 with respect to the depositionmedia as it is envisaged that, in some embodiments, the head 10 mayremain stationary while deposition media are transported past the head10 (e.g. using a conveyor belt, a reel, paper feed or the like), whereasin other embodiments the head 10 may be moved (e.g. by being attached toa motorised carriage) while the deposition medium remains stationary(e.g. as in some rapid prototyping or 3D printing applications). Indeed,combinations of both approaches might also be employed in still otherembodiments (e.g. as in a scanning printhead in a printer).

In the particular example embodiment shown in FIG. 1, the depositionmedia speed data 310 is received by the head controller circuitry 200.However, this is not essential and in other embodiments the head 10and/or the actuating circuitry 100 might be configured to receive thedeposition media speed data 310.

The current speed of relative movement may be indicated in thedeposition media speed data 310 in any suitable way. For instance, thedeposition media speed data 310 might simply include a value for thecurrent speed of the relative movement in a predetermined unit.Alternatively, the deposition media speed data 310 correspond to thelength of time taken for the deposition media to move a predeterminedincrement in distance relative to the head 10, or, conversely, thedeposition media speed data 310 correspond to the distance that thedeposition media have moved relative to the head in a predeterminedincrement in time (for example, the media speed data may be provided bydetecting a signal based on the registration marks of a rotarypositional encoder associated with a moving media web).

The droplet deposition apparatus uses the deposition media speed data310 to decide when to switch from ejecting droplets in accordance withone sub-set of ejection data to ejecting droplets in accordance with thenext sub-set of ejection data in the series. Specifically, thisswitching occurs at a time determined in accordance with the currentspeed of relative movement of the head with respect to the depositionmedia, as indicated by said media speed data. Furthermore, the timeinterval between starting ejecting droplets in accordance withsuccessive sub-sets of ejection data varies inversely with the currentspeed of relative movement of the head.

This switching is illustrated in FIGS. 2A and 2B. For instance, inaccordance with sub-set 210(1) of ejection data, the actuating circuitry100 causes nozzles 18(1), 18(2), 18(6) and 18(7) to eject droplets.Then, the apparatus switches to ejecting droplets in accordance withsub-set 210(2) of ejection data, which causes nozzles 18(3)-18(6) toeject droplets. The apparatus then switches to ejecting droplets inaccordance with sub-set 210(3) of ejection data, which causes nozzles18(1)-18(3) and 18(7) to eject droplets. Thereafter, the apparatusswitches to ejecting droplets in accordance with sub-set 210(4) ofejection data, which causes nozzles 18(5)-18(7) to eject droplets, andthen switches to ejecting droplets in accordance with sub-set 210(5) ofejection data, which causes nozzles 18(1)-18(7) to eject droplets. Ineach case, an arrow at the top of the drawing indicates that theapparatus will shortly thereafter switch to the indicated sub-set ofejection data.

FIGS. 3A and 3B illustrate the ejection of droplets in accordance withthe same series of sub-sets of ejection data 210(1)-210(5), but in asituation where the speed of relative movement of the head with respectto the deposition media varies in a different way with respect to time.As a result of this different variation in speed with respect to time,the deposition media speed data 310 received by the apparatus will bedifferent in each case.

In more detail, in the example shown in FIG. 2A, the speed of relativemovement of the head increases shortly after the head starts ejectingdroplets in accordance with sub-set 210(3) of ejection data. The speedremains at this new, higher level while droplets are ejected inaccordance with sub-sets 210(4) and 210(5) of ejection data.

By contrast, in the example shown in FIG. 3A, the speed of relativemovement of the head increases shortly after the head starts ejectingdroplets in accordance with sub-set 210(2) of ejection data. The speedthen remains at this new, higher level while droplets are ejected inaccordance with sub-set 210(3) of ejection data, but then returns (slowsdown) to the original level shortly after the head has started ejectingdroplets in accordance with sub-set 210(4) of ejection data.

As noted above, the time interval between starting ejecting droplets inaccordance with successive sub-sets of ejection data 210(1)-210(5)varies inversely with the current speed of relative movement of thehead. This is apparent from comparing the different points in time forthe arrows at the top of FIG. 2A and the arrows at the top of FIG. 3A.

Attention is now directed to FIGS. 2B and 3B, which show the pattern ofdroplets formed on the deposition medium in each case. As is apparent,where the speed of relative movement increases, so does the spacingbetween consecutive rows based on the same sub-set of ejection data. Forinstance, in FIG. 2B, spacing s₁ between rows deposited in accordancewith sub-set 210(1) is smaller than spacing s₂ between rows deposited inaccordance with sub-set 210(3). Similarly, in FIG. 3B, spacing s₁between rows deposited in accordance with sub-set 210(1) is smaller thanspacing s₂ between rows deposited in accordance with sub-set 210(2).

However, as a result of the inverse relationship between the speed ofrelative movement and the time interval between starting ejectingdroplets in accordance with successive sub-sets of ejection data, forthe droplets corresponding to any two sub-sets of ejection data, thedistance (in the direction of relative movement) between the first andlast row of droplets is approximately the same. For instance, in FIG.2B, the distance l₁ between the first and last rows of dropletsdeposited in accordance with sub-set 210(1) is approximately the same asthe distance l₂ between the first and last rows of droplets deposited inaccordance with sub-set 210(3). This is because, as noted above, therows deposited in accordance with sub-set 210(3) have a greater spacings₂.

Similarly, in FIG. 3B, the distance l₁ between the first and last rowsof droplets deposited in accordance with sub-set 210(1) is approximatelythe same as the distance l₂ between the first and last rows of dropletsdeposited in accordance with sub-set 210(2), because the rows depositedin accordance with sub-set 210(2) have a greater spacing 52.

It will accordingly be understood that a droplet deposition apparatus asdescribed herein may be capable of maintaining generally the same size(in the direction of relative movement of the head) for the variousparts of a desired pattern of droplets, despite variations in the speedof relative movement of the head. Such variations in speed may, forexample, result from variable performance of the systems or mechanismsthat move the head relative to the deposition media, or may result froma user deliberately increasing the speed of relative movement whiledeposition is occurring (e.g. part way through depositing droplets ontoa large number of articles, such as labels, cans, bottles etc., so as tofinish the run by the end of the work-day).

In some embodiments, the time interval discussed above may besubstantially inversely proportional to the current speed of relativemovement (or substantially so). Accordingly, a doubling in speed wouldlead to a halving of the time interval between sending successivesub-sets of ejection data. (In practice however, such changes in speedmay be introduced incrementally such that they are not noticeable byeye, and are particularly well tolerated where the overall depositionvolume of droplets is high.)

In other embodiments, the time interval may be determined by applying amore complex mathematical function or procedure to the deposition mediaspeed data 310. For instance, such a function might include terms thatare time derivatives or integrals of the current speed (or estimatesthereof). For example, such a function might include a termcorresponding to the current rate of change in the speed (i.e. thecurrent acceleration) of the deposition media with respect to the head.This may, in effect, enable the head controller circuitry 200 toanticipate imminent changes in the speed of relative movement. Toaccomplish this, the actuating circuitry 100 might, for example, store acertain amount of recent deposition media speed data 310 (e.g. in a databuffer).

As noted above, for each sub-set of ejection data 210(1)-210(5), theactuating circuitry 100 causes the repeated ejection of droplets fromparticular nozzles, thus depositing successive rows of droplets on themedium. As also noted above, droplets according to the current sub-set210(1)-210(5) of ejection data stop being ejected when the head switchesto ejecting droplets in accordance with a consecutive sub-set210(1)-210(5) of ejection data. In some embodiments, the actuatingcircuitry 100 may be configured so as to cease the repeated ejection ofdroplets in accordance with the current sub-set of ejection data once atleast one of the one or more nozzles ejecting droplets has ejected Mx(or more) droplets, Mx corresponding to a suitably large maximum numberof droplets. In addition, or instead, the current sub-set 210(1)-210(5)of ejection data may stop being ejected in response to the actuatingcircuitry 100 receiving a “stop” command, for example as a result of afault condition and/or as a result of user input. Such a “stop” commandmay take precedence over other interrupt conditions.

There will now be described a particular example of an approach forusing the deposition media speed data 310 to control switching fromejecting droplets in accordance with one sub-set of ejection data toejecting droplets in accordance with the next sub-set of ejection datain the series.

As noted above, in the particular example embodiment shown in FIG. 1,the deposition media speed data 310 is received by the head controllercircuitry 200. Thus, the head controller circuitry 200 receives bothinput data 610 and deposition media speed data 310. As also noted above,the head controller circuitry 200 acts to generate a series of sub-sets210(1)-(3) of ejection data based on the input set 610 and sends theseto the actuating circuitry 100. The inventors contemplate that theapparatus may be configured so as to conveniently use each sub-set210(1)-(3) of ejection data as a trigger signal, which causes theactuating circuitry 100 to start ejecting droplets in accordance withthe recently arrived sub-set of ejection data 210(1)-(3) at the nextavailable opportunity.

For example, this may be accomplished by suitable configuration of theactuating circuitry 100, for instance so that it implicitly treats thearrival of a sub-set 210(1)-(3) of ejection data as a trigger signal.Alternatively, this may, for example, be accomplished by including witheach sub-set of ejection data 210(1)-(3) a code indicating that dropletsin accordance with the data should be ejected straightaway (sometimesreferred to as a “fire code”).

To accomplish switching using sub-sets 210(1)-(3) of ejection data astrigger signals, the inventors propose that the time interval betweensending successive sub-sets 210(1)-(3) of ejection data should varyinversely with the current speed of relative movement. Thus, where thedeposition media speed is increased, the frequency with which sub-sets210(1)-(3) of ejection data are required to be sent to the actuatingcircuitry 100 will likewise need to increase (and, conversely, therequired time interval between the sending of successive sub-sets ofejection data will need to decrease). Such an inverse relationship maylead to droplets from any two sub-sets 210(1)-(3) of ejection dataoccupying respective areas on the deposition medium that have similarlengths in the direction of relative movement, despite changes in thespeed of relative movement.

This particular approach to switching is implemented in the examplesillustrated in FIGS. 2A-2B and 3A-3B. Specifically, the arrows in FIG.2A and FIG. 3A may be understood as indicating the time at which theindicated sub-set 210(1)-(5) of ejection data arrives at the actuatingcircuitry 100. As is apparent, shortly after each sub-set 210(1)-(5) ofejection data arrives at the actuating circuitry 100, the nozzles18(1)-(7) eject droplets in a corresponding pattern.

As noted above, each nozzle ejects droplets with a substantiallyconstant frequency of 1/T. The head 10 may be considered as operating inaccordance with an actuation cycle during which each of the one or morenozzles determined by the current sub-set of ejection data ejects asingle droplet. Where a sub-set of ejection data arrives at theactuating circuitry 100 part-way through such an actuation cycle, theactuating circuitry 100 may be configured to wait until the currentactuation cycle is completed before applying drive waveforms accordingto the recently received sub-set of ejection data. For instance, in FIG.2A, sub-set 210(4) arrives half-way through an actuation cycle and theactuating circuitry 100 therefore waits until droplets are ejected fromeach of nozzles 18(1)-(3) and 18(7), which correspond to the currentsub-set 210(3) of ejection data.

To facilitate this, the actuating circuitry 100 may include a buffer forstoring newly-arrived sub-sets of ejection data until the currentactuation cycle is completed. Moreover, in some embodiments, this buffermay be used to signal the actuating circuitry 100 to switch to ejectingdroplets in accordance with a newly-arrived sub-set of ejection data.For instance, the actuating circuitry 100 may cause the head to continueejecting droplets in accordance with a current sub-set of ejection datauntil the buffer indicates that it has received a newly-arrived sub-setof ejection data.

In the particular example embodiment illustrated in FIG. 1, the inputset of ejection data 610 represents a two-dimensional array of dropletejection values 615. Such droplet ejection values may, for example,indicate the volume of droplets to be ejected (e.g. taking integralvalues between 0 and M, where 0 corresponds to no droplet being ejectedand M corresponds to a droplet having a maximum size), or they mayindicate a particular group of nozzles within the array (e.g. nozzleswhose corresponding actuating elements 22 should be actuated in aparticular manner). Each member of the two-dimensional array 615 mayindeed include a respective value corresponding to each of a number ofdifferent types of ejection values.

Each droplet size value may take any integer value between 0 and M.Alternatively, each droplet size value may be either 0 or M, optionallywhere M=1. In embodiments, such as that shown in FIG. 1, where the inputset of ejection data 610 represents a two-dimensional array of dropletejection values 615, consecutive sub-sets of ejection data in the series(e.g. 210(1) and 210(2), or 210(2) and 210(3)) may be determined basedon successive slices 616(1)-616(3) of the two dimensional array. Theordering of the slices 616(1)-616(3) may thus be the same as theordering of the resulting sub-sets of ejection data 210(1)-210(3). As isapparent from the drawing, in the particular example embodiment shown inFIG. 1, each slice 616(1)-616(3) is a linear array, i.e. only one arraymember wide (though this is not essential and the slices could insteadbe two or more members wide).

Thus, each of the slices of the two dimensional array may be aone-dimensional array.

In generating the sub-sets of ejection data 210, various data processingmight take place. For instance, where each row (or column) of the inputset of ejection data 610 corresponds to a respective nozzle in the head10, each sub-set of ejection data might simply represent the ejectionvalues in that row (or column). Alternatively, some conversion may takeplace, for example in the case where it is desired that each of thesub-sets of ejection data 210 represents ejection values on aper-actuating element 22 basis, i.e. with an ejection value for eachactuating element 22, rather than each nozzle 18.

Attention is now directed to FIG. 4, which is a block diagram thatillustrates schematically a droplet ejection apparatus according to afurther example embodiment. The droplet deposition apparatus of FIG. 4is based on that illustrated in FIG. 1 and therefore operates insubstantially the same way, except insofar as is described below.

As may be seen from the drawing, the droplet deposition apparatus shownin FIG. 4 includes a droplet deposition head 10, as well as associatedactuating circuitry 100 and head controller circuitry 200, similarly tothe droplet deposition apparatus of FIG. 1. However, in contrast to thedroplet deposition apparatus of FIG. 1, the example embodiment of FIG. 4further includes a media transport system 500 and a server 600. Theserespectively provide deposition media speed data 310 and dropletejection data 610 to the head controller circuitry 200.

As before, the deposition media speed data 310 indicates the currentspeed of relative movement of the head 10 with respect to the depositionmedia the deposition media speed data 310, whereas the droplet ejectiondata 610 represents a two-dimensional array of values 615 for dropletcharacteristics.

As illustrated in FIG. 4, the deposition media speed data 310 mayinclude data representing a deposition media speed value. As discussedabove, this may correspond to the current speed in a particularpredetermined unit (e.g. m/s), the length of time taken for thedeposition media to move a predetermined increment in distance relativeto the head 10, or the distance that the deposition media have movedrelative to the head in a predetermined increment in time (for example,the media speed data may be provided by detecting a signal based on theregistration marks of a rotary positional encoder associated with amoving media web).

As is further illustrated in FIG. 4, the media transport system 500 mayinclude a number of motors 520, such as for driving a conveyor belt,reel, or paper feed (e.g. in embodiments where the head 10 remainsstationary while the deposition media are moved), or for driving acarriage to which the head 10 is attached (e.g. in embodiments where thehead 10 is moved while the deposition media remain stationary).

As also shown, the media transport system 500 may further include arotary encoder 510, which provides a signal indicating the currentrotational position of a rotating element within the media transportsystem 500, such as an axle in a conveyor belt or reel. This signal fromthe rotary encoder 510 may, for example, be sent to the head controllercircuitry 200 as media speed data 310. Alternatively, the signal fromthe encoder 510 could be processed (e.g. by one or more processorsforming part of the media transport system 500) so as to provide acurrent speed value, with the media speed data 310 sent by the mediatransport system 500 comprising data representing the thus-calculatedspeed value.

As to the server 600, this may convert data provided by the user intosuitable droplet ejection data 610 for use within the apparatus. Forinstance, where the droplet deposition apparatus is configured as aprinter, the user might, for example, provide data in the form of animage file, with the server 600 converting this data into correspondingdroplet ejection data 610, for example by using a raster image processor(RIP) (which may be implemented as software running on general purposeprocessors of server 600, or as a dedicated processor). This conversionmay, for example, involve reducing the tone resolution of the data (asimages will typically have 256 available levels for each pixel, whereasprintheads will typically only have up to 8 sizes available for eachdroplet), while simultaneously increasing the spatial resolution of thedata, to compensate for the reduction in tone resolution. Analogous dataconversion processes may run on the server 600 where the dropletdeposition apparatus is configured for other applications, such as rapidprototyping or 3D printing applications.

FIG. 4 additionally shows the drive waveforms 110(3) and 110(N) appliedrespectively to actuators 22(3) and 22(N). As may be seen, each drivewaveform 110 includes a number of pulses; however, the drive waveform110(3) applied to actuator 22(3) includes fewer pulses than the drivewaveform 110(N) applied to actuator 22(N). The volume of the dropletejected in response to each drive waveforms is positively related to thenumber of pulses, as is schematically illustrated by the differentlysized droplets ejected by corresponding nozzles 18(3) and 18(N). Withsuitable design of the drive waveforms the droplet volume may begenerally proportional to the number of pulses in the drive waveform110.

FIG. 5 is a block diagram that illustrates a further example embodimentof a droplet deposition apparatus, which is generally described abovewith reference to FIGS. 1 and 4, but where the actuating circuitry 100is provided by two separate components.

As shown in the drawing, the actuating circuitry 100 may be consideredas comprising actuation control circuitry 120 and waveform generatingcircuitry 110. The actuation control circuitry 120 receives a series ofsub-sets 210(1)-(3) of ejection data from head controller circuitry 200,generally in the manner described above.

For each such sub-set 210(1)-(3) of ejection data, the actuation controlcircuitry 120 generates a corresponding set of actuation commands. Eachset of actuation commands is then sent repeatedly to the waveformgenerating circuitry 110, which is provided as part of (i.e. on-board)the head 10. Each set of actuation commands causes the waveformgenerating circuitry 110 to apply drive waveforms to the actuatingelements 22(1)-(N) of the head 10 such that they eject a droplet fromcertain of the nozzles 18(1)-(N). The particular nozzles 18(1)-(N) andthe sizes of the droplets ejected therefrom are determined by the set ofactuation commands, and therefore the associated sub-set 210(1)-(3) ofejection data.

In this way, the sending of each such set of actuation commands leads tothe deposition of a corresponding row of droplets on the medium.Accordingly, the repeated sending of a particular set of actuationcommands leads to the deposition of successive rows of droplets on themedium. As before, this involves each of the nozzles repeatedly ejectingdroplets at a substantially constant frequency of 1/T.

At a general level, the actuation control circuitry 120 may be regardedas receiving trigger signals and switching between sets of actuationcommands in response. More particularly, it switches from sendingactuation commands in accordance with the current sub-set 210(1)-(3) ofejection data to sending actuation commands in accordance with theconsecutive sub-set of ejection data 210(1)-(3) in the series at a timedetermined in accordance with such trigger signals.

In the particular example embodiment shown in FIG. 5, the arrival ofeach sub-set 210(1)-(3) of ejection data implicitly acts as acorresponding trigger signal, and thus causes the actuation controlcircuitry 120 to start sending a set of actuation commands in accordancewith the sub-set of ejection data at the next available opportunity(e.g. once the current actuation cycle for the head has been completed).However, in other embodiments the actuation circuitry 120 might beconfigured to receive deposition media speed data 310 (e.g. byconnection to a rotary encoder 510 as described above with reference toFIG. 4), with such deposition media speed data 310 providing the triggersignals for switching between sets of actuation commands.

FIG. 6 illustrates a further example embodiment, where the actuatingcircuitry 100 is again provided by two separate components, though in adifferent manner to that illustrated in FIG. 5. Specifically, theactuation control circuitry 120 of the actuating circuitry 100 (whichgenerates sets of actuation commands, generally in the same manner asdescribed above with reference to FIG. 5) and the head controllercircuitry 200 are both provided on an ejection data processing component20. As with the example embodiment of FIG. 5, the waveform generatingcircuitry 110 is provided as part of (i.e. on-board) the head 10.

Accordingly, it will be understood from the example embodiments of FIG.1, FIG. 5 and FIG. 6 suitable head controller circuitry 200, waveformgenerating circuitry 110, actuation control circuitry 120 may beimplemented using various combinations of components, such as variousarrangements of integrated circuits (e.g. application-specificintegrated circuit, ASIC's, field programmable gate arrays, FPGA's,system on chip, SoC, devices).

From the generality of the foregoing description, it will be understoodthat the apparatus, circuitry and methods disclosed herein may utilise awide range of droplet deposition heads. Solely by way of example, headsas disclosed in the Applicant's earlier patent publications WO00/38928,WO2007/113554, WO2016/001679, WO2016/156792, WO2016/193749,WO2017/118843 might be utilised.

Though the foregoing description has presented a number of examples, itshould be understood that other examples and variations are contemplatedwithin the scope of the appended claims.

It should be noted that the foregoing description is intended to providea number of non-limiting examples that assist the skilled reader'sunderstanding of the present invention and that demonstrate how thepresent invention may be implemented.

The invention claimed is:
 1. Controller circuitry for a dropletdeposition head that comprises an array of actuating elements and acorresponding array of nozzles, the controller circuitry configured to:receive an input set of ejection data; generate a series of sub-sets ofejection data based on the input set; receive deposition media speeddata, which indicates the current speed of relative movement of thedroplet deposition head with respect to the deposition media; and sendsaid series of sub-sets of ejection data and respective ejectioncommands to actuating circuitry for the droplet deposition head, theejection commands being sent at a time determined in accordance with thecurrent speed of relative movement of the droplet deposition head withrespect to the deposition media as indicated in said deposition mediaspeed data, the time interval between sending successive sub-sets ofejection data varying generally inversely with the current speed ofrelative movement of the droplet deposition head; wherein the actuatingcircuitry is configured so as to, for each set of ejection commands,apply drive waveforms to said actuating elements so as to repeatedlyeject droplets from one or more of said nozzles, thus depositingsuccessive rows of droplets, the one or more nozzles and the sizes ofthe droplets ejected therefrom being determined by the current sub-setof ejection data, wherein each of the one or more nozzles maintain theejection of droplets with a substantially constant frequency of 1/T inaccordance with successive sub-sets of ejection data.
 2. The controllercircuitry according to claim 1, wherein each sub-set of ejection dataimplicitly acts as the respective actuation command.
 3. The controllercircuitry according to claim 1, wherein each sub-set of ejection data issent simultaneously with the corresponding actuation command.
 4. Thecontroller circuitry according to claim 1, wherein said input set ofejection data represents a two-dimensional array of droplet ejectionvalues; and wherein consecutive sub-sets of ejection data in said seriesare determined based on successive slices of said two dimensional array.5. The controller circuitry according to claim 1, wherein each sub-setof ejection data defines, for each nozzle, a corresponding value for thesize of droplets to be ejected by that nozzle, each droplet size valuebeing between 0, corresponding to no ejection, and M, corresponding to amaximum droplet size.
 6. The controller circuitry according to claim 5,wherein each droplet size value can take any integer value between 0 andM.
 7. The controller circuitry according to claim 5, wherein eachdroplet size value can be either 0 or M.
 8. The controller circuitryaccording to claim 1, configured to generate substantially the whole ofsaid series of sub-sets of ejection data prior to sending said series ofsub-sets of ejection data to the actuating circuitry.
 9. A method fordepositing droplets using a droplet deposition head comprising an arrayof actuating elements and a corresponding array of nozzles, the methodcomprising: receiving an input set of ejection data; generating a seriesof sub-sets of ejection data based on the input set; receivingdeposition media speed data, which indicates the current speed ofrelative movement of the droplet deposition head with respect todeposition media; and operating the droplet deposition head according toeach sub-set of ejection data in turn, while moving the dropletdeposition head relative to the deposition media, such operatingcomprising: for each sub-set of ejection data, repeatedly ejectingdroplets from one or more nozzles within said array so as to depositsuccessive rows of droplets, the one or more nozzles and the sizes ofthe droplets ejected therefrom being determined by the current sub-setof ejection data, each of the one or more nozzles ejecting droplets witha substantially constant frequency of 1/T; and switching from ejectingdroplets in accordance with one sub-set of ejection data to ejectingdroplets in accordance with the consecutive sub-set of ejection data ata time determined in accordance with the current speed of relativemovement of the droplet deposition head with respect to the depositionmedia as indicated by said media speed data, the time interval betweenstarting ejecting droplets in accordance with successive sub-sets ofejection data varying inversely with the current speed of relativemovement of the droplet deposition head, wherein each of the one or morenozzles maintain the ejection of droplets with a substantially constantfrequency of 1/T in accordance with successive sub-sets of ejectiondata.
 10. The method according to claim 9, wherein said input set ofejection data represents a two-dimensional array of droplet ejectionvalues; and wherein consecutive sub-sets of ejection data in said seriesare determined based on successive slices of said two dimensional array.11. The method according to claim 9, wherein each sub-set of ejectiondata defines, for each nozzle, a corresponding value for the size ofdroplets to be ejected by that nozzle, each droplet size value beingbetween 0, corresponding to no ejection, and M, corresponding to amaximum droplet size.
 12. The method according to claim 11, wherein eachdroplet size value can take any integer value between 0 and M.
 13. Themethod according to claim 11, wherein each droplet size value can beeither 0 or M.
 14. The method according to claim 9, wherein thesubstantially the whole of said series of sub-sets of ejection data isgenerated prior to sending said series of sub-sets of ejection data tothe actuating circuitry.
 15. The method according to claim 9, furthercomprising ceasing said repeated ejection of droplets determined by thecurrent sub-set of ejection data once at least one of the one or morenozzles ejecting droplets has ejected Mx droplets, where Mx correspondsto a maximum number of droplets.
 16. The method according to claim 9,further comprising ceasing said repeated ejection of droplets determinedby the current sub-set of ejection data in response to a “stop” command.17. The method according to claim 9, wherein, for each of the one ormore nozzles that repeatedly ejects droplets in accordance with thecurrent sub-set of ejection data, each such droplet ejected from thenozzle in question is of substantially the same size.
 18. The methodaccording to claim 9, wherein, for each nozzle that ejects droplets inaccordance with successive sub-sets of ejection data, the time intervalbetween the final droplet resulting from the earlier set and the firstdroplet resulting from the later set is substantially equal to T. 19.The method according to claim 9, wherein, in response to each sub-set ofejection data, the droplet deposition head operates in accordance withan actuation cycle, during which each of the one or more nozzlesdetermined by the current sub-set of ejection data ejects a droplet.